The present research proposal is concerned with the experimental study of cardiovascular and associated physiological responses of laboratory dogs trained on operant conditioning tasks that require them to inhibit behavioral activity and maintain increases in total peripheral resistance in order to avoid the onset of conditioned aversive stimuli. Short-term experiments will be performed to determine effects of these conditioning procedures upon heart rate, stroke volume, cardiac output, arterial and venous pressure and total peripheral resistance, using chronically implanted cardiovascular sensors and a computerized system for data recording and reduction. In addition, effects upon baroreceptor reflex activity and the role of the autonomic effector system in the mediation of the observed hemodynamic patterns will be investigated. Long-term experiments over periods of six months will be conducted to determine the effects upon arterial blood pressure of repeatedly exposing experimental subjects to environmental settings that elicit behavioral inhibition and associated circulatory changes characterized by increases in total peripheral resistance and decreased or unchanged cardiac output.